川西亚高山针叶林土壤酶及其化学计量比对模拟氮沉降的响应

Response of soil enzyme activity and stoichiometric ratio to simulated nitrogen deposition in subalpine coniferous forests of western Sichuan

大气氮沉降的明显增加将有可能显著影响我国西部地区受氮限制的亚高山森林生态系统的物质循环.为了解模拟氮沉降会不会改变土壤酶活性及其化学计量比并缓解该区域土壤微生物生长代谢对氮的限制,选择川西亚高山60年生的四川红杉(Larix mastersiana)人工林为研究对象,通过4个水平梯度的土壤模拟氮沉降控制试验(CK:0 g m-2 a-1;N1:2 g m-2 a-1;N2:5 g m-2 a-1;N3:10 g m-2 a-1),检测7种土壤酶活性及其化学计量比.结果表明:N-乙酰葡萄糖苷酶、过氧化物酶、C:NEEA、N:PEEA对一个生长季模拟氮沉降有显著响应,特别在模拟氮沉降后期表现为中氮显著促进N-乙酰葡萄糖苷酶活性(56.40%-204.78%)、过氧化物酶活性(42.28%-54.87%);酸性磷酸酶、β-葡萄糖苷酶、纤维二糖酶、亮氨酸酶、多酚氧化酶、土壤酶化学计量碳磷比(C:PEEA)对一个生长季施氮无显著响应,但都具有极显著月动态.相关分析和逐步回归分析表明,土壤温度和含水率是土壤酶活性及其化学计量比的决定性因子.综上所述,研究区域亚高山森林土壤微生物的碳氮磷代谢对模拟氮沉降响应显著,微生物代谢呈现出一定的氮限制,模拟氮沉降中氮水平后期微生物代谢呈现出由氮限制向磷限制转化的趋势.

The increasing atmospheric nitrogen deposition maybe significantly affect the material circulation of subalpine forest ecosystems, where alpine soils are generally restricted by nitrogen in western China. The aim of the presents study was to examine whether simulated nitrogen deposition would change the soil enzyme activity and its stoichiometry and alleviate the nitrogen limitation of soil microbial metabolism in this region. Four gradient experiments of simulated nitrogen deposition (CK: 0 g m-2 a-1;N1: 2 g m-2 a-1;N2: 5 g m-2 a-1;N3: 10 g m-2 a-1) were conducted in the 60-year-old Larix mastersiana plantation of the subalpine forest in western Sichuan, to analyze the activity of seven soil enzymes and the stoichiometric ratio. The results indicated that N-acetylglucosidase, peroxidase, C:NEEA, and N:PEEA had a significant response to simulated nitrogen deposition in the growing season, and medium simulated nitrogen deposition elicited a significant promotion of N-acetylglucosidase 56.40%-204.78% and peroxidase 42.28%-54.87%, especially in the later growing season. Acid phosphatase,β-glucosidase, cellobiase, leucine, polyphenol oxidase, and C:PEEA did not exhibit a significant response to simulated nitrogen deposition in the growing season, but all enzymes had significantly monthly variations. Correlation analysis and stepwise regression analysis revealed that soil temperature and moisture content were the decisive factors for soil enzyme activity and stoichiometric ratios. The carbon, nitrogen, and phosphorus metabolism of soil microorganisms responded significantly to simulated nitrogen deposition, and microbial metabolism showed a certain degree of nitrogen restriction in subalpine coniferous forests. The microbial metabolism showed a trend of conversion from nitrogen restriction to phosphorus restriction at the later stage of medium simulated nitrogen deposition.